Fluid dispensing system having independently operated pumps

ABSTRACT

A fluid dispensing system is provided which has a first diaphragm pump, a filter connected to receive the discharge of said first pump, and an accumulator/second diaphragm pump connected to receive the discharge of said filter. Hydraulic fluids pumped by cylinder/piston/stepper assemblies independently actuate each of the diaphragm pumps, providing accurate, controllable and repeatable dispense of the subject fluid. The system further includes a suck-back device downstream of the second pump.

This is a continuation of application Ser. No. 09/106,586, filed Jun.29, 1998, now U.S. Pat. No. 6,105,829, which is a continuation ofapplication Ser. No. 08/605,878, filed Feb. 23, 1996, now U.S. Pat. No.5,772,899, which is a continuation of application Ser. No. 08/107,866,filed on Aug. 18, 1993, now U.S. Pat. No. 5,516,429, which is acontinuation of application Ser. No. 07/747,884, filed on Aug. 20, 1991,now abandoned, which is a continuation of application Ser. No.07/329,525, filed Mar. 28, 1989 now U.S. Pat. No. 5,167,837.

BACKGROUND OF THE INVENTION

This invention relates to a pumping system useful in dispensing fluids,especially those which are expensive, viscous, high purity, and/orsensitive to molecular shear.

The invention has numerous applications, but is especially useful in themicroelectronics industry. The trend in that industry is to squeezegreater quantities of circuitry onto smaller substrates. Circuitgeometries have been shrunk to less than one micron. In that microscopicworld, the slightest particle of contamination can create a defect,decreasing production yields, degrading device performance, and reducingdevice reliability.

For this and other reasons, modern manufacturing techniques in themicroelectronics and other industries sometimes involve decontaminated“cleanroom” environments. Many of these techniques also use advancedprocess chemicals, some of which are very expensive. For example,certain chemicals used to process semiconductors can cost $15,000 ormore per gallon, and the semiconductor substrates can be worth $20,000or more at that stage of processing. To be useful in cleanroomenvironments and applications, however, the chemicals must be filtered.Because of the viscosities and sensitivities of the fluids, they must befiltered at low flow rates and under low pressure to minimize molecularshear on the fluids. Prior art devices do not meet these parameters incertain production-line operations.

For example, some operations require a periodic, non-continuous “shot”of fluid. Such “shots” sometimes consume only a small part of the pump'scycle time, leaving the pump and/or filter idle during the remainder ofthe cycle. During that relatively brief moment when a shot occurs, highpressure must be used to achieve a flow rate sufficient to dispense anappropriate amount of fluid. As noted above, such high pressures andflow rates can damage sensitive fluids.

In addition, low pressure filtration is generally recognized as the bestway to effectively eliminate gel slugs in, and remove contaminants from,a subject fluid. If high pressure is used to achieve a desired flow ratethrough a filter, contaminants can be forced through the filter, ratherthan retained therein.

Furthermore, many operations, especially in the semiconductor industry,apply only small amounts of fluid to each unit processed. In theseapplications, there is an increased need for precise control over thedispense.

Additionally, the reservoir of subject fluid needs to be easilymonitored, replaced, and/or replenished. These dispense systems alsoneed to be easily primed with and purged of subject fluid, to allow thesystem to be used on more than one fluid, and to reduce fluid shear.

At the present time there is no system that satisfactorily meets thesevarious requirements. In fact, in some research laboratories, theseexpensive fluids are still being dispensed by hand; that is, labtechnicians or scientists pour the fluids directly out of storagecontainers. This hand pouring has poor repeatability, involvessignificant operator technique, does not allow point-of use filtration,and generally causes a tremendous, expensive waste of time andmaterials. Production and laboratory costs could be greatly reduced byautomating the dispense of these fluids.

Numerous other problems exist with prior art dispense systems. Incertain operations where relatively high pressure is acceptable anddesired to achieve a necessary flow rate, such as through a filter whichis still useful even though partially clogged, prior art systems cannotdeliver, or are inaccurate when delivering, the required pressure. Thesystems have poor predictability and repeatability of results. Theircomplicated flowpaths are difficult to purge, and excessive fluidhold-up volumes lead to fluid waste.

Prior art systems also waste fluid during dispensing and provide little,if any, in the way of “suck-back” adjustment. Suck-back is an adjustmentmade at the outlet port of a given dispense system, in which the fluidis drawn back slightly inside the port. This adjustment reduces fluidsolvent evaporation at the outlet during idle periods, reduces fluidcontamination at the outlet, and most importantly allows for a sharp anddripless cessation of dispense, avoiding waste of the processed fluid.

Additionally, prior art systems are not easily automated, their fluidreservoir levels cannot be easily monitored, and they are limited in therange of fluid viscosities which they can dispense. Finally, complexmechanisms downstream of the filter often generate fluid contaminants.

For example, certain prior art systems utilize diaphragm-type pumpswhich the diaphragm is actuated by air pressure. Typically, theactuating air is more compressible than the liquids being pumped. As airpressure is increased in an attempt to displace the diaphragm anddispense fluid, the actuating air is compressed, in effect “absorbing”part of the intended displacement of the diaphragm. This air compressionprevents accurate control and monitoring of the position of thediaphragm and, correspondingly, prevents accurate control and monitoringof the volume and rate of fluid dispensed.

The problem is exacerbated if the fluid is being pumped through afilter. By its nature, the filter becomes clogged during use. As itbecomes clogged, higher pressure is required to achieve a given flowrate through the filter. Because the air pressure actuating thediaphragm typically remains relatively constant throughout the life ofthe filter, however, fluid flow rate through the filter decreases as thefilter becomes more clogged, making it even more difficult to achieverepeatable, accurate dispense.

OBJECTS AND ADVANTAGES OF THE INVENTION

It is, therefore, an object of our invention to provide a fluiddispensing system which can accurately and repeatedly dispense withoutcontaminating a subject fluid.

Another object of our invention is to provide a fluid dispensing systemwhich can be utilized in filtering viscous and other fluids underrelatively low pressure, decreasing molecular shear on the fluids. Apreferred embodiment of the invention allows the fluid to be filteredcontinuously (and thus at a relatively low pressure and flow rate) withone pump, while being dispensed non-continuously with a second pump.

It should be understood that, while the invention is described herein inconnection with dispense of high-purity, viscous fluids, the inventionmay be utilized in many other applications. Moreover, although thepreferred embodiment discussed herein includes two pumping means withfilter means interposed therebetween, advantageous aspects of theinvention may be practiced with no filter means, or with only onepumping means with or without filter means.

Another object of our invention is the provision a dispensing systempermitting the use of computer or other automated control for the rateand interval of dispense, as well as for the direction of fluid flowthrough the system and fluid pressure during operation of the system.

Still another object of our invention is the provision of a dispensingsystem which permits great flexibility of operation, making it adaptableto numerous applications.

An additional object of our invention is to provide a pumping systemwhich can be easily purged of a processed fluid.

Yet another object of our invention is to provide a fluid filteringsystem with no contamination-generating components downstream from thefilter.

Still another object of our invention is to provide a pumping systemwhich can dispense fluids at controlled flow rates without beingaffected by the condition of a filter within the system, even ifrelatively high pressure is required to achieve the flow rates.

An additional object of our invention is to provide a pumping systemwhich can accurately provide and control suck-back of process fluid, andcan be primed and/or recharged with minimal waste, stress, shear orintroduction of gasses into the process fluid.

Another object of our invention is to provide a pumping system in whichthe fluid input reservoir may be replenished or otherwise adjustedwithout interrupting the dispense operation of the system, and in whichthe reservoir fluid input level can be easily monitored.

Other objects and advantages of the invention will be apparent from thefollowing specification and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a dispensing system constructed inaccordance with the teachings of the invention; and

FIG. 2 is a schematic, partially sectional side elevation view of apreferred embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring to the drawings, and particularly to FIG. 1 thereof, we show apreferred embodiment of a dispense system 10 constructed in accordancewith the teachings of the invention. In broad terms, a subject fluid(the fluid to be dispensed) enters system 10 from a reservoir throughtubing 14, travels through valve means 20 to first pumping means 30,returns through valve means 20 to filter means 100, travels throughsecond pumping means 120, and is dispensed through tubing 16. A moredetailed explanation of its operation is set forth below.

A housing 12, FIG. 1, has sides 11 and a mounting plate 13 forming thetop thereof. The sides 11 and mounting plate 13, as well as many of theother components of the preferred embodiment, are typically constructedof stainless steel in order to be compatible with laboratory andcleanroom environments and with the subject fluids.

Valve means 20, FIG. 2, is incorporated in a valve member 22,exemplified as a ball valve 24 mounted on plate 13. Ball valve 24includes valve body 23 with ball element 25 and ports 26, 27, and 28therein. Ball element 25 can be selectively rotated to permit fluidcommunication either between ports 26 and 27 or ports 27 and 28. Thisselective rotation can be accomplished by various means, including valveactuating means 29. In the preferred embodiment, actuating means 29 isan electronic valve drive motor which permits remote and/orcomputer-controlled actuation of ball valve 24.

First pumping means 30 includes a first pumping member 32, constitutingmaster diaphragm pump 34 mounted on plate 13, first incremental pumpmeans 50, and tubing 51 therebetween. Pump 34 includes upper housing 38machined from stainless steel, lower housing 40 machined from aluminum,and teflon\ diaphragm 36 disposed therebetween. Those skilled in the artwill understand that materials other than stainless steel, aluminum andteflon\ may be used in the practice of the invention. Diaphragm 36 isretained in sealing engagement between upper and lower housings 38 and40 at least in part by sealing ring 42, which is disposed betweenhousings 38 and 40 at their mutual peripheries.

Housings 38 and 40 are so machined that, when assembled with diaphragm36 and sealing ring 42, a pumping chamber 45 is formed between saidhousings, said chamber being divided by diaphragm 36 into an uppercompartment 44 and a lower compartment 48. Upper compartment 44 isdefined by diaphragm 36 and internal surface 39 of upper housing 38.Internal surface 39 is shaped so that diaphragm 36 can, whensufficiently deflected, conform thereto. When so deflected, the capacityof compartment 44 is nil, all fluid having been purged therefrom.

Passage 43 is machined in upper housing 38 to establish fluidcommunication between port 46 and upper compartment 44. Port 46 isconnected by tubing 41 to port 27 of ball valve 24, permitting fluidflow between valve means 20 and first pumping means 30. Port 47, withtubing 51 connected thereto, is provided in lower housing 40 to permitexternal fluid communication with lower compartment 48.

In the preferred embodiment, pumping means 30 includes a pressure sensor49 in fluid communication with lower compartment 48 to monitor thepressure therein. Sensor 49, the function of which is more fullyexplained below, can be connected to a computer or other automaticcontrol to assist in operation of dispense system 10. In an alternativeembodiment, a second pressure sensor may be similarly positioned andemployed on the second pumping means 120.

Lower compartment 48 is filled with a relatively incompressible fluidsuch as hydraulic coupling fluid, which communicates through port 47 andtubing 51 with first incremental pump advancement means 50.

Incremental pump advancement means 50, FIG. 2, incorporates a hydraulicstepper assembly 54, comprising housing components 55 and 59 connectedby cylindrical coupling 57, and electronic stepper motor 62 connected tocomponent 59. In the preferred embodiment, the structure and operationof advancement means 50 is identical to the structure and operation ofsecond incremental advancement means 90, shown as hydraulic stepperassembly 94. The internal structure and the function of incrementaladvancement means 50 can be conveniently illustrated, therefore, byreference to stepper assembly 94, shown in FIG. 2 in partial sectionalview.

Stepper assembly 94 includes components 85 and 89, corresponding tocomponents 55 and 59 of advancement means 50. Components 85 and 89 arereleasably connected by cylindrical coupling 87 to form cylinder 64.Piston 66 is machined from hard chrome-plated stainless steel and isslidably disposed in cylinder 64, reciprocating therein in response torotation of lead screw linear drive 80. A bore 67 is axially disposed inthe piston 66 to receive the drive 80. A ball nut 83 is operablyattached to piston 66 at the mouth of the bore 67, and the drive 80 isthreadedly engaged with the ball nut 83 to cause the aforesaidreciprocation of piston 66 in cylinder 64. Drive 80 is actuated byelectronic stepper motor 72, through its output shaft 70, flexible shaftcoupling 74, bearing pre-load nut 76, and dual thrust bearings 78. Shaft70, coupling 74, nut 76, bearings 78, drive 80, ball nut 83, and piston66 are all assembled to translate the rotational movement of outputshaft 70 into linear movement of piston 66.

Piston anti-rotation bearing 82 is fixedly connected to piston 66 andslidably disposed in slot 81, to prevent rotation of piston 66 incylinder 64. As piston 66 reciprocates in cylinder 64, bearing 82correspondingly reciprocates in slot 81, which is axially oriented inone side of housing component 89. Energized teflon scraper seals 86 andbronze piston guides 84 are located adjacent the juncture of housingcomponents 85 and 89. Seals 86 and guides 84 are retained in annulargrooves in the wall of cylinder 64, to prevent fluid leakage fromcylinder 64 and to guide piston 66 in cylinder 64.

Electronic stepper motor 72 may be controlled by a computer or someother form of automatic control, and may be selectively operated tocause right-hand or left-hand rotation of shaft 70. As indicated above,this rotation causes corresponding linear movement of piston 66 incylinder 64. Motor 72 is operable in finite, repeatable and controllableincrements and rates, allowing corresponding control of the movement ofpiston 66.

Piston 66 has an end 65 which, together with cylinder 64, defineschamber 68. Chamber 68 is filled with a relatively incompressible fluidsuch as hydraulic coupling fluid. Housing component 85 includes port 69which provides fluid communication between chamber 68 and tubing 123.

Second pumping means 120 is shown in FIG. 2 as pump member 122,constituting slave diaphragm pump 124, and second incremental pumpadvancement means 90 connected by tubing 123 to pump 124. Slave pump 124includes upper and lower housing components 125 and 127, diaphragm 126,and sealing ring 121, which correspond respectively to housingcomponents 38 and 40, diaphragm 36, and ring 42 of master pump 34. Slavepump 124 also includes lower compartment 128 and upper compartment 131,similar to compartments 48 and 44, respectively, of master diaphragmpump 34.

Port 129 is machined in lower housing 127, and tubing 123 is connectedthereto, to provide fluid communication between lower compartment 128and port 69 of chamber 68. Compartment 128, tubing 123, and chamber 68are filled with a relatively incompressible fluid such as hydrauliccoupling fluid. Similarly, their corresponding components in firstadvancement means 50 and first diaphragm pump 34 are filled withhydraulic coupling fluid.

Because diaphragm 36 of first pump member 32 is actuated in a similarmanner to the actuation of diaphragm 126 in second pump member 122, adiscussion of the latter is illustrative of both. As piston 66 isreciprocated in cylinder 64, coupling fluid is selectively either forcedfrom chamber 68 through tubing 123 to compartment 128, or withdrawn inthe opposite direction by relative negative pressure (a partial vacuum)in chamber 68. These alternative fluid conditions, in turn, causecorresponding alternative deflection of diaphragm 126. This displacementof diaphragm 126 is volumetrically equivalent to the displacement ofpiston 66.

Movement of diaphragm 126 can be accurately controlled because theabove-discussed precise movements of piston 66 are transmitted todiaphragm 126 with relatively no distortion through the hydraulic fluidmedium. As noted above, movements of diaphragm 126 are relativelyaccurate and repeatable in comparison to prior art dispense pump systemswhich use, for example, compressible fluids such as air to deflectdiaphragm 126.

Diaphragm pump 34 can be primed with subject fluid by rotating ballelement 25 to place port 27 in fluid communication with port 28, asshown in FIG. 2. Stepper assembly 50 is operated to deflect diaphragm 36to minimize the capacity of compartment 44. Next, ball element 25 isrotated so that port 27 communicates with port 26. Advancement means 50is then operated to deflect diaphragm 36 to maximize the capacity ofcompartment 44, creating relative negative pressure therein, as comparedto atmospheric. This relative negative pressure pulls fluid from areservoir through tubing 14, ball valve 24, and tubing 41 intocompartment 44. The process is continued until all air is purged fromcompartment 44, tubing 14, and tubing 41.

During both the initial priming operation of the system and thesubsequent stages of processing in which the compartment 44 is rechargedwith the subject fluid, the rate of deflection of diaphragm 36 isclosely controlled to limit the amount of relative negative pressurecreated in compartment 44. The pressure is monitored by pressure sensor49, and the operation of advancement means 50 is adjusted accordingly.This close control is necessary to prevent “outgassing” in the subjectfluid. If the negative pressure becomes excessive, undesirable gaspockets may form in the subject fluid.

In the preferred embodiment, the maximum capacity of compartment 44 isgreater than the combined capacities of passage 43, tubing 41, andtubing 14, which enhances purging and priming operations of system 10.Also, pressure sensor 49 can be used to monitor the relative negativepressure to prevent outgassing in the subject fluid when the fluid isbeing drawn into compartment 44.

Filter means 100 is shown in FIG. 2 as filter member 106, constituted byteflon\ fluid filter element 108 removably located in chamber 110 formedin upper housing component 38. Chamber 110 has two ports, inlet port 112and outlet port 114, positioned on opposite extremities of filterelement 108. Passage 111 is machined in housing 38 to provide fluidcommunication between port 112 and port 104. Tubing 102 connects ports104 and 28.

After master pump 34 has been primed with subject fluid, ball element 25is rotated to place ports 27 and 28 in fluid communication with oneanother. In the preferred embodiment, pump 34 can then pump fluid tofilter means 100 through port 28, tubing 102, port 104, passage 111 andport 112. The pumped fluid then travels through filter element 108 inchamber 110, and out of chamber 110 through outlet port 114.

Those skilled in the art will understand that alternative embodiments ofthe invention would include filter means 100 remote from upper housing38, as well as no filter element at all.

After exiting chamber 110 through port 114, the subject fluid flowsthrough tubing 116 to port 117 of slave diaphragm pump 124. As indicatedabove, the basic structure and function of slave diaphragm pump 124 areidentical to master diaphragm pump 34. At least one importantdistinction exists, however, in that upper housing component 125 ofsecond pump 124 has separate inlet and outlet passages 118 and 119providing fluid access to compartment 131. Passages 118 and 119 aremachined in housing component 125 to provide fluid communication betweenupper compartment 131 and ports 117 and 130 respectively. Outlet tubing16 is connected to port 130.

The subject fluid enters upper compartment 131 through port 117 andpassage 118, and can be selectively: (1) accumulated in uppercompartment 131 for subsequent dispense; (2) dispensed immediatelythrough passage 119 and port 130 to tubing 16; or (3) partiallyaccumulated and partially dispensed. This flexibility of operationinheres in master pump's 34 use as a filtration pump independently fromslave pump's 124 use as a fluid accumulator/dispense pump. The selectedoperation of system 10 is achieved through coordinated control ofdiaphragms 126 and 36 by advancement means 90 and 50, respectively.

To accumulate filtered fluid in slave pump 124, diaphragm 126 is drawndown at a rate at least as great as the rate at which fluid is beingpumped through passage 118 by master pump 34.

The capacities of upper compartments 131 and 44 of their respectivediaphragm pumps 124 and 34 are approximately equivalent, and aretypically greater than the volume of subject fluid required during anysingle dispense, for applications involving periodic dispense of fluid.For this reason, master pump 34 can be utilized to draw and filter thesubject fluid independently of whether fluid is being dispensed fromsystem 10. Compartment 131 can, in effect, serve as a storage chamberfor filtered fluid.

This means that subject fluid may be filtered at a slower rate (therebyreducing molecular shear on the fluid) than might be required in, forexample, a “shot” type of periodic dispense. By way of illustration, ifa production line cycle requires two seconds of dispense followed bythree seconds of non-dispense, system 10 allows each volume of fluid tobe filtered over a span of five seconds. During the three seconds ofnon-dispense, fluid is accumulated in slave pump 124. In contrast, iffluid were to be dispensed directly from filter means 100, only twoseconds would be available to filter the same volume of fluid,necessitating an increase in flow rate of, and pressure on, the fluid.In short, first pumping means 30 can pump fluid through filter means 100at a rate and for an interval completely independent of the rate andinterval at which the subject fluid is dispensed from the second pumpingmeans 120.

Dispense of the subject fluid can be controlled solely by actuation ofdiaphragm 126, after sufficient subject fluid has been filtered andaccumulated in compartment 131. To do so, ball valve 24 is actuated toallow communication between inlet port 26 and port 27, effectivelyblocking flow through tubing 102. With the ball valve 24 in thisposition, second pumping means 120 can selectively dispense fluidthrough passage 119. Even if ports 27 and 28 are in communication witheach other, fluid will not flow back through tubing 102 if pumping means30 remains static. Additionally, pumping means 120 can “suck-back” thefluid from outlet tubing 16 through port 130. Advancement means 90 isoperated to “pull down” diaphragm 126, enlarging compartment 131 andcreating a relative negative pressure therein. As noted above, this“suck-back” process provides many benefits, including preventing wastageof material, preventing unnecessary contamination of the fluid, andimproving the accuracy of the dispense of the fluid. If diaphragm 126 ispulled down at a sufficiently high rate, suck-back can be achieved evenwhile fluid is being filtered and pumped into compartment 131.Furthermore, while valve 24 connects ports 26 and 27, the fluidreservoir connected to tubing 14 can be replaced or otherwise alteredwithout affecting or interrupting the dispense of fluid from outlet port130.

Filter element 108 and the various ports and tubing throughout system 10are selected and sized based on, among other factors, the viscosities,allowable molecular shear, and desired flow rates of the subject fluids.Those skilled in the art will understand that a given filter element 108and tubing and port sizing will perform satisfactorily for a range offluid viscosities and flow rates.

As system 10 is used, particle contaminants in the subject fluid arecollected in filter element 108, gradually blocking the flow of subjectfluid. As this blockage increases, fluid flow rate through filterelement 108 will decrease unless the pressure differential across filterelement 108 is increased.

In some prior art systems, the pressure differential across the filteris limited by the pressure available to actuate the diaphragm pump. Inthe preferred embodiment, however, because relatively incompressiblefluid is used in lower compartment 48 and throughout the relevant ports,tubing and advancement means 50, there is no corresponding limitation ondifferential pressure applied across filter element 108. Assuming thatthe subject fluid is also relatively incompressible, flow rate acrossfilter element 108 is controlled by the movement of piston 66 inadvancement means 50. In effect, a given volumetric displacement ofpiston 66 results in an equivalent volumetric displacement of diaphragm36. Although incoming fluid pressure may increase as filter element 108becomes blocked through use, the rate and amount of fluid flow areunaffected by such blockage; that is, an incremental rate or amount ofmovement of piston 66 will result in a corresponding rate and amount offluid flow through filter element 108.

Those skilled in the art will understand that the invention can also bepracticed where a single chamber houses both diaphragm 36 and piston 66of advancement means 50, eliminating the intervening ports and tubing51.

As indicated above, increased pressure may be necessary to achieve agiven flow rate as filter element 108 becomes clogged. Pressure sensor49 allows any such increases in pressure to be monitored, and alsothereby indirectly indicates the amount of blockage in filter element108. Pressure levels can be determined which will indicate when filterelement 108 needs to be replaced, as well as when maximum allowableshear on the subject fluid is being approached.

As further indicated above, pressure sensor 49, actuating means 29, andadvancement means 50 and 90 can all be connected to an automated control(such as a computer), permitting automatic, repeatable, preciseoperation of system 10. The precision and flexibility of such a controlarrangement far surpasses anything available in the prior art. Such acomputer-controlled arrangement also allows computer monitoring of thevolume of fluid dispensed by systen 10, as well as volume drawn in fromthe fluid reservoir. For example, the relative movements of electronicstepper motor 62 can be monitored by computer. As noted above, thosemovements correspond to the volume of subject fluid being pumped fromupper compartment 44 of master diaphragm pump 34. If the volume of fluidin the reservoir is known and input into the computer, the computer canalso indicate when the reservoir is nearing depletion.

Those skilled in the art will understand that certain principles of theinvention may be practiced without any second pumping means 120, inwhich case fluid would be dispensed from tubing 116. This arrangement isuseful where fluid viscosity is relatively low, blockage of filterelement 108 requires a relatively long period of time, and dispense ofthe fluid is to be non-continuous; that is, where the desired dispensecan be achieved without accumulating the fluid in a post-filteringchamber such as chamber 131.

Similarly, those skilled in the art will understand that certainprinciples of the invention may be practiced without any filter means100 between first pumping means 30 and second pumping means 120. In suchsituations, port 28 of ball valve 24 could be connected by tubing toport 117 of second pumping means 120.

Additionally, certain aspects of the invention may be practiced by theuse of the first pumping means 30 without second pumping means 120, andeither with or without filter means 100. Such an arrangement wouldprovide precise, repeatable dispense of fluid, and could be used inapplications involving less viscous fluids or fluids which do notrequire point-of-use filtration.

What is claimed is:
 1. A method of dispensing a fluid for use within themicroelectronics industry, including the steps of: pumping said fluidwith first pumping means; receiving said fluid by operating secondpumping means; dispensing said fluid from an outlet downstream of saidsecond pumping means; and sucking-back fluid downstream of said secondpumping means.
 2. The method of claim 1 further comprising filteringsaid fluid prior to said fluid being received by said second pumpingmeans.
 3. The method of claim 1 in which said fluid is one or more ofviscous high purity and shear sensitive.
 4. A substantially defect-freemicroelectric substrate, said substrate fabricated by a step of applyinga precise volume of fluid thereto, said precise volume pumped by asystem comprising first and second pumping means in series and structureoperable to suck-back fluid from downstream of said second pumpingmeans.
 5. The substrate of claim 4 further comprising filtering saidfluid prior to being received by said second pumping means.